MammographyJ HK Coll Radiol for 2003;6:126-131 Early Breast Cancer Detection REVIEW ARTICLE CME Advances in Mammography Have Improved Early Detection of Breast Cancer KH Ng,1 M Muttarak2 1Department of Radiology, University of Malaya, Kuala Lumpur, Malaysia 2Department of Radiology, Chiang Mai University, Chiang Mai, Thailand ABSTRACT Breast cancer remains a leading cause of death among women throughout the world. The incidence is in- creasing globally and the disease remains a significant public health problem. Mammography is currently the best method to detect early breast cancer before it becomes clinically palpable. The use of mammography results in a 25% to 30% decreased mortality rate in screened women compared with controls after 5 to 7 years. Today’s dedicated mammographic equipment with specially designed X-ray screen/film combinations coupled with controlled film processing produces excellent image quality mammograms. It is important to produce reliable high-contrast, high-resolution images for mammography. Both the American College of Radiology Mammography Accreditation Program and the Mammography Quality Standards Act have had significant impact on the technical quality of mammographic images in the USA and worldwide. The recent development in digital mammography has opened the possibility for improving diagnosis and novel applications. This article reviews the major technical developments that led to today’s high quality mammograms. Key Words: Digital radiography, Image quality, Mammography, Quality control Early Detection of Breast Cancer Mammography is currently the best method to detect Breast cancer remains a leading cause of death for early breast cancer before it becomes clinically palpable. women throughout the world. It is the most common The use of mammography results in a 25% to 30% malignancy among women in developed countries and decreased mortality rate in screened women compared the second or third most common malignancy among with controls after 5 to 7 years.3 A recent update of the women in developing countries.1 The incidence of breast experience of the Swedish 2-county screening trial at cancer is increasing globally and the disease remains 20 years follow-up shows a significant 32% reduction a significant public health problem. The prognosis in mortality.4 Controversy has arisen about the age at of breast cancer is related to the stage of the disease which regular screening should begin. Many countries at diagnosis and treatment. The earlier the tumour is in Europe recommend biennial screening for women detected, the better the prognosis. Routine screening for aged 50 years and older but many professional organi- breast cancer for asymptomatic women can detect sations in the USA recommend screening every 1 to 2 clinically non-palpable tumours resulting in a survival years for women aged 40 to 49 years, and annual screen- rate of 95.1% after almost 20 years.2 Early detection of ing for women aged 50 years and older.5 breast cancer also permits less aggressive therapeutic options such as lumpectomy followed by radiation Although screening mammography has become well therapy as opposed to mastectomy, and a decreased need accepted,2-4 2 recently published articles by Danish for systemic chemotherapy. researchers Gotzche and Olsen concluded that mam- mography is ineffective for reducing breast cancer Correspondence: Professor KH Ng, Department of Radiology, mortality.6,7 Despite the opinions of these researchers, University of Malaya, Kuala Lumpur, Malaysia. many investigators and organisations still recommend Tel: (60 3) 7950 2088; Fax: (60 3) 7958 1973; screening mammography beginning at the age of 40 Email: [email protected] years with annual screening intervals because early Submitted: 19 May 2003; Accepted: 9 July 2003. detection through screening mammography has 126 J HK Coll Radiol 2003;6:126-131 KH Ng, M Muttarak undoubtedly played a role in breast cancer mortality Technical Advances in Mammography reduction.5,8-12 Although screen film mammography (SFM) is good, it is neither perfectly sensitive nor highly specific. It has Before the widespread use of screening mammography, important limitations in detecting subtle soft tissue le- ductal carcinoma in situ (DCIS) was considered a sions that represent breast carcinoma, especially in the relatively uncommon lesion, accounting for only 0.85% presence of dense breast tissue. Because many carcino- to 5.0% of all breast carcinomas.13 Since the recent intro- mas are undetected, there are ongoing efforts to improve duction of screening mammography, DCIS accounts the ability of mammography to detect cancers earlier. for 30% to 45% of all detected cancers. The dramatic increase in incidence of DCIS can be explained by the There have been significant advances in mammographic introduction of screening mammography.14 Microcalcifi- X-ray equipment and in screen/film recording systems cations are an especially important sign of early breast during the past 25 years.16-18 Until the mid 1980s, many cancer since they are the dominant abnormality in 90% X-ray units were not dedicated mammography systems. of in situ carcinomas.15 Any measure that improves These units had tungsten target tubes that were origin- the mammographic demonstration or the radiologist’s ally designed for other medical imaging procedures perception of microcalcifications should improve de- such as chest radiography. Many of these units had tection of DCIS. Technical advances in mammography home-made compression devices that could not ensure equipment have led to significant improvement in mam- adequate compression of the breast. Many of these units mographic image quality and changed the ability to had large focal spots or short focal spot-to-breast sur- detect early breast carcinoma (Figure 1). face distances that could result in significant geometric (a) (b) Figure 1. Routine craniocaudal mammogram versus spot-magnification mammogram. (a) Right craniocaudal mammogram shows a clustered of microcalcifications in the outer quadrant and (b) spot-magnification mammogram shows better details of microcalcifications, which are linear and branching. Histology revealed ductal carcinoma in situ, comedo type. J HK Coll Radiol 2003;6:126-131 127 Mammography for Early Breast Cancer Detection blur (unsharpness). Direct exposure (industrial type) X-ray films were being used, which often required long 2.0 exposure times (causing blur by motion) and that Infiltrative ductal tissue Fibrous tissue resulted in high radiation exposure. In addition, view- Adipose tissue ing conditions were inadequate. ) 1.0 -1 Today, mammography is performed with dedicated 0.8 mammography X-ray equipment.16-18 These units have specially designed X-ray tubes, smaller focal spots, and 0.6 significantly improved breast compression devices, among other features. Modern X-ray tubes have multi- 0.4 ple targets of tungsten, molybdenum, and rhodium that are selected by microprocessor to give optimum tissue penetration. Cassettes and special films and intensify- ing screens are designed especially for mammography. (cm Linear attenuation coefficient 0.2 Film processing has been the major weak link giving rise to image quality problems and artifacts. Never- theless this has also significantly improved over time. Today, it is possible to obtain mammograms with higher 0.1 20 40 60 80 100 image quality at a significantly lower radiation dose Energy (keV) compared with 25 years ago. In 2000, the first digital mammography system was approved by the USA Food Figure 2. Attenuation coefficients of various breast tissues.19 and Drug Administration (FDA) for clinical use. Table 1 lists the historical milestones in technical advances in various components of the breast. The sigmoidal char- mammography. acteristic curve (Figure 3) is such that the contrast is high for intermediate exposure areas but low for both Image Quality of Mammograms low and high exposures. In other words, ‘thin’ and Obtaining optimum image quality in mammography ‘dense’ areas of the breast are displayed with low con- is technically very demanding, especially since this trast; but this is improved with digital mammography. impacts on the accuracy of the diagnosis. Figure 2 shows measured X-ray attenuation coefficients of Quality Control Regulations in Maintaining fibroglandular breast tissue, fat, and breast carcinoma Standard versus X-ray energy.19 The small difference between Since the American Cancer Society guidelines for early the curves illustrate why mammography is such a detection of breast cancer have become widely accepted challenging imaging task, particularly when the tumour by the medical community, and because some facilities is surrounded by fibroglandular tissue. The limited were known to produce poor quality mammograms, dynamic range of film-screen mammography presents in 1987, the American College of Radiology (ACR) a serious limitation in detecting and recording the developed the Mammography Accreditation Program Table 1. Historical milestones in technical advances in mammography.16-18 Year Development Organisation Before 1969 Conventional tungsten target X-ray tubes with direct exposure industrial type film 1969 Dedicated mammographic unit with molybdenum target tube and compression Compagnie Generale Radiologie device Senographe 1971 Xeromammography Xerox 1972 Screen-film system Du Pont Lo-dose system 1976 Rare earth screen-film system and special cassette Kodak Min-R system 1977 Magnification with microfocal spot Radiological Sciences Inc. 1978 Grid